Hypertrophic cardiomyopathy 2 (CMH2) is the TNNT2-related form of familial hypertrophic cardiomyopathy. TNNT2 encodes cardiac troponin T (cTnT), the tropomyosin-binding subunit of the heterotrimeric troponin complex that, together with troponin C and troponin I, transduces the calcium signal into tropomyosin movement and crossbridge cycling on the thin filament. TNNT2 was one of the two genes, together with TPM1, whose 1994 discovery established hypertrophic cardiomyopathy as a disease of the sarcomere, and cardiac troponin T mutations accounted for roughly 15% of familial HCM in the founding referral-centre cohort. CMH2 is molecularly and clinically distinctive among the sarcomeric HCM series: disease-associated variants, most classically Arg92Gln/Trp/Pro in the tropomyosin-binding domain, act as dominant "poison peptides" that sensitize the thin filament to calcium and are incorporated whether the carrier is asymptomatic or not. The clinical signature that follows is the "malignant but mild" phenotype first described for the Arg92 hotspot: left ventricular wall thickness is frequently only mildly or subclinically increased, yet the incidence of sudden cardiac death is disproportionately high relative to the degree of hypertrophy, making genotype-informed risk assessment - rather than wall-thickness measurement alone - especially important for carriers of these variants. Not every TNNT2 allele follows this pattern: variant-specific studies (for example the founder variant p.Asn271Ile) show that some TNNT2 alleles instead produce late-onset, low-risk disease, so genotype-phenotype correlation in CMH2 is stated at the level of the individual variant rather than the gene as a whole.
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name: Hypertrophic Cardiomyopathy 2
creation_date: "2026-08-17T00:00:00Z"
synonyms:
- CMH2
- TNNT2 hypertrophic cardiomyopathy
- hypertrophic cardiomyopathy caused by mutation in TNNT2
- hypertrophic cardiomyopathy type 2
- cardiomyopathy, hypertrophic, 2
- cardiomyopathy, familial hypertrophic, type 2
- familial hypertrophic cardiomyopathy type 2
description: >-
Hypertrophic cardiomyopathy 2 (CMH2) is the TNNT2-related form of familial
hypertrophic cardiomyopathy. TNNT2 encodes cardiac troponin T (cTnT), the
tropomyosin-binding subunit of the heterotrimeric troponin complex that,
together with troponin C and troponin I, transduces the calcium signal into
tropomyosin movement and crossbridge cycling on the thin filament. TNNT2 was
one of the two genes, together with TPM1, whose 1994 discovery established
hypertrophic cardiomyopathy as a disease of the sarcomere, and cardiac
troponin T mutations accounted for roughly 15% of familial HCM in the
founding referral-centre cohort. CMH2 is molecularly and clinically
distinctive among the sarcomeric HCM series: disease-associated variants,
most classically Arg92Gln/Trp/Pro in the tropomyosin-binding domain, act as
dominant "poison peptides" that sensitize the thin filament to calcium and
are incorporated whether the carrier is asymptomatic or not. The clinical
signature that follows is the "malignant but mild" phenotype first described
for the Arg92 hotspot: left ventricular wall thickness is frequently only
mildly or subclinically increased, yet the incidence of sudden cardiac death
is disproportionately high relative to the degree of hypertrophy, making
genotype-informed risk assessment - rather than wall-thickness measurement
alone - especially important for carriers of these variants. Not every TNNT2
allele follows this pattern: variant-specific studies (for example the founder
variant p.Asn271Ile) show that some TNNT2 alleles instead produce late-onset,
low-risk disease, so genotype-phenotype correlation in CMH2 is stated at the
level of the individual variant rather than the gene as a whole.
category: Genetic
classifications:
harrisons_chapter:
- classification_value: CARDIOVASCULAR
- classification_value: GENETICS_ENVIRONMENT_DISEASE
disease_term:
preferred_term: hypertrophic cardiomyopathy 2
term:
id: MONDO:0007266
label: hypertrophic cardiomyopathy 2
parents:
- Hypertrophic Cardiomyopathy
- Genetic Disorder
prevalence:
- population: Familial hypertrophic cardiomyopathy referral cohorts
measure_type: UNKNOWN
prevalence_class: NOT_YET_DOCUMENTED
notes: >-
No population-based prevalence estimate exists for the TNNT2-specific form
of hypertrophic cardiomyopathy. What is documented is the share of HCM
cases attributable to TNNT2, which is a minority but larger than most other
non-MYH7/MYBPC3 sarcomere genes: roughly 15% of familial cases in the
founding referral-centre survey. The population occurrence of hypertrophic
cardiomyopathy as a whole (about 1 in 500) is curated on the umbrella
Hypertrophic Cardiomyopathy entry and is not duplicated here.
evidence:
- reference: PMID:7898523
reference_title: Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mutations in cardiac troponin T account for approximately 15 percent of
cases of familial hypertrophic cardiomyopathy in this referral-center
population.
explanation: >-
Quantifies the TNNT2 share of familial HCM cases in the founding
referral-centre cohort.
inheritance:
- name: Autosomal Dominant
description: >-
CMH2 is transmitted as an autosomal dominant trait. ClinGen's Hereditary
Cardiovascular Disease Gene Curation Expert Panel classifies the
TNNT2-hypertrophic cardiomyopathy relationship as Moderate with autosomal
dominant inheritance (an older, 2021 SOP7 curation, in contrast to the
Definitive classifications now recorded for MYH7, MYBPC3, and TPM1 - see
notes). Penetrance by echocardiographic criteria is incomplete and lower
than for MYH7, and disease-associated variants are frequently incorporated
into the sarcomere while producing only mild or subclinical hypertrophy,
which is itself part of the CMH2 phenotype rather than evidence against
pathogenicity.
inheritance_term:
preferred_term: Autosomal dominant inheritance
term:
id: HP:0000006
label: Autosomal dominant inheritance
penetrance: INCOMPLETE
evidence:
- reference: CGGV:assertion_ef922dc4-4e41-422b-ac3d-605fea375005-2021-02-04T050000.000Z
reference_title: "TNNT2 / hypertrophic cardiomyopathy (Moderate)"
supports: SUPPORT
evidence_source: OTHER
snippet: >-
TNNT2 | HGNC:11949 | hypertrophic cardiomyopathy | MONDO:0005045 | AD |
Moderate
explanation: >-
ClinGen's Hereditary Cardiovascular Disease GCEP records autosomal
dominant inheritance for the TNNT2-hypertrophic cardiomyopathy
relationship with Moderate clinical validity.
- reference: PMID:32731933
reference_title: Penetrance of Hypertrophic Cardiomyopathy in Sarcomere Protein Mutation Carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
At 15 years follow-up, estimated HCM penetrance by causal gene was as
follows: MYBPC3 43% (95% CI: 32% to 57%), MYH7 66% (95% CI: 47% to 83%),
TNNI3 17% (95% CI: 7% to 39%), TNNT2 50% (95% CI: 30% to 74%), TPM1 42%
(95% CI: 11% to 92%)
explanation: >-
Gene-specific penetrance estimate for TNNT2 (50% at 15 years). Quoted
with its full confidence interval, which overlaps every other gene in the
table, so the point estimate should not be counselled as sharply
distinguishing TNNT2 from the other sarcomere genes.
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
maximal ventricular wall thickness 11.3 +/- 5.4 mm) and low disease
penetrance by clinical criteria (40% by echocardiography) but a high
incidence of sudden cardiac death (mean age 17 +/- 9 years).
explanation: >-
Direct pedigree-level statement of low echocardiographic penetrance
combined with minimal hypertrophy for the Arg92Trp founder variant,
establishing that low penetrance by imaging is a feature of CMH2 rather
than an artifact of ascertainment.
- reference: PMID:37929589
reference_title: "Meta-Analysis of Penetrance and Systematic Review on Transition to Disease in Genetic Hypertrophic Cardiomyopathy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Penetrance varied from ≈32% for MYL3 (myosin light chain 3) to ≈55% for
MYBPC3 (myosin-binding protein C3), ≈60% for TNNT2 (troponin T2) and
TNNI3 (troponin I3), and ≈65% for MYH7 (myosin heavy chain 7).
explanation: >-
A contemporary, larger meta-analytic estimate of TNNT2 penetrance in
cascade-screened relatives (~60%), corroborating the earlier
PMID:32731933 estimate (50% at 15 years) with a substantially larger
evidence base (455 manuscripts assessed) and placing TNNT2 penetrance
between MYBPC3 and MYH7 among the sarcomere genes.
genetic:
- name: TNNT2
gene_term:
preferred_term: TNNT2
term:
id: hgnc:11949
label: TNNT2
relationship_type: CAUSATIVE
frequency: >-
A minority but comparatively common cause of familial hypertrophic
cardiomyopathy after MYBPC3 and MYH7 - approximately 15% of cases in the
founding referral-centre survey.
case_fractions:
- population: Familial HCM referral-centre cohort (Watkins et al.)
case_fraction_percent: 15.0
notes: >-
Historical estimate from the first systematic screen of cardiac troponin
T in HCM probands and families.
evidence:
- reference: PMID:7898523
reference_title: Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mutations in cardiac troponin T account for approximately 15 percent
of cases of familial hypertrophic cardiomyopathy in this
referral-center population.
explanation: >-
Direct quantitative statement of the TNNT2 case fraction in familial
HCM.
evidence:
- reference: PMID:8205619
reference_title: "Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Missense mutations (Ile79Asn; Arg92Gln) and a mutation in the splice
donor sequence of intron 15 of the cardiac troponin T gene are also
shown to cause FHC.
explanation: >-
The original gene-disease assertion establishing TNNT2 as causative for
familial hypertrophic cardiomyopathy, including the founding Arg92Gln
allele.
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A novel cardiac troponin T gene mutation, arginine 92 tryptophan, was
identified in 19 of 48 members of two affected pedigrees.
explanation: >-
Independent confirmation of a second missense allele at the codon 92
hotspot cosegregating with disease in two large pedigrees.
- reference: CGGV:assertion_ef922dc4-4e41-422b-ac3d-605fea375005-2021-02-04T050000.000Z
reference_title: "TNNT2 / hypertrophic cardiomyopathy (Moderate)"
supports: SUPPORT
evidence_source: OTHER
snippet: >-
TNNT2 | HGNC:11949 | hypertrophic cardiomyopathy | MONDO:0005045 | AD |
Moderate
explanation: >-
ClinGen classifies the TNNT2-hypertrophic cardiomyopathy gene-disease
relationship as Moderate.
- reference: PMID:40310325
reference_title: The p.Asn271Ile Variant in the TNNT2 Gene Is Associated With Low-Risk Late-Onset Hypertrophic Cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Late-onset HCM and incomplete age-related penetrance were observed
(estimated median diagnosis age 60.1 years). ... Codon 92 variants'
carriers (76 individuals, 28 probands) had a higher penetrance, being
diagnosed 19.4 years earlier, and they exhibited a significantly worse
prognosis (primary endpoint in 34.3%; P < 0.001).
explanation: >-
Documents that TNNT2 genotype-phenotype correlation must be made at the
allele level: the founder variant p.Asn271Ile is low-risk and
late-onset, in direct contrast to the malignant codon-92 hotspot
variants that define the classic CMH2 phenotype.
notes: >-
Disease-associated TNNT2 variants for CMH2 are overwhelmingly missense and
concentrate in the tropomyosin-binding N-terminal and central regions of
cardiac troponin T, with codon 92 (Arg92Gln, Arg92Trp, Arg92Pro/Leu) as the
best-characterized hotspot for the malignant, minimal-hypertrophy
phenotype. Other alleles cited in this entry with human genotype-phenotype
data: Ile79Asn, K280N (reported homozygous), E163R, and the low-risk
founder variant p.Asn271Ile. A splice-donor mutation in intron 15,
predicted to act as a null allele, was among the original TNNT2 alleles
reported and was used to argue that abnormal sarcomeric protein
stoichiometry, not only a poison-peptide mechanism, can produce the
phenotype.
mechanistic_hypotheses:
- hypothesis_group_id: tnnt2_calcium_sensitization_uncoupling
hypothesis_label: Myofilament calcium sensitization with loss of PKA-mediated desensitization
status: CANONICAL
description: >-
The canonical model of CMH2 is that HCM-associated TNNT2 variants are
incorporated into the thin filament as poison peptides that increase
myofilament calcium sensitivity - a near-universal finding across the
disease-associated alleles studied to date, from the founder R92Q mutation
in transgenic mice to recombinant and patient-derived troponin carrying
K280N, DeltaE160, S179F, and other substitutions. A second, recurring
feature specific to several TNNT2 (and other thin-filament) HCM mutations
is "uncoupling": normal cardiac troponin I phosphorylation by protein
kinase A lowers myofilament calcium sensitivity as part of the lusitropic
(relaxation-enhancing) response to adrenergic stimulation, but mutant
troponin T blunts or abolishes this modulation, removing a physiological
brake on calcium sensitivity precisely when it is most needed.
evidence:
- reference: PMID:27036851
reference_title: Mutations in troponin T associated with Hypertrophic Cardiomyopathy increase Ca(2+)-sensitivity and suppress the modulation of Ca(2+)-sensitivity by troponin I phosphorylation.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
The R92Q TnT mutation in troponin from transgenic mouse increased
Ca(2+)-sensitivity and was also completely uncoupled.
explanation: >-
Directly demonstrates both halves of the canonical mechanism - increased
calcium sensitivity and uncoupling from troponin I phosphorylation - for
the founding R92Q CMH2 allele.
- reference: PMID:37159677
reference_title: Low expression of the K280N TNNT2 mutation is sufficient to increase basal myofilament activation in human hypertrophy cardiomyopathy.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Myofilament Ca2+-sensitivity was higher in homozygous cTnT-K280N
cardiomyocytes and was not corrected by AP- and PKA-treatment. ... A low
level (14%) of the cTnT-K280N sensitizes myofilaments to Ca2+, a
universal finding of human HCM.
explanation: >-
Human explanted-myocardium and isogenic hiPSC-cardiomyocyte study
showing that even a low mutant protein fraction (14%) is sufficient to
raise calcium sensitivity, and that PKA treatment does not correct it -
corroborating the uncoupling component of the mechanism directly in
human tissue rather than only in transgenic mice.
- hypothesis_group_id: tnnt2_variant_specific_ec_coupling_divergence
hypothesis_label: Mutation-specific balance between myofilament and excitation-contraction coupling remodeling
status: ALTERNATIVE
description: >-
A second, complementary account holds that the relative contribution of
primary myofilament dysfunction versus secondary excitation-contraction
(E-C) coupling remodeling to the CMH2 phenotype is mutation-specific rather
than uniform across the gene. In paired mouse models, the R92Q allele
produced comparatively modest myofilament-level sarcomeric changes beyond
calcium sensitization but profound secondary E-C coupling remodeling
(blunted inotropic reserve, slowed calcium-transient decay, reduced SERCA
function, increased CaMKII activity), whereas the E163R allele produced
prominent primary myofilament abnormalities (altered sarcomere energetics,
elevated resting tension) with comparatively preserved calcium handling.
Both alleles converge on diastolic dysfunction and arrhythmogenicity, but
by different routes, with implications for which class of therapy -
sarcomere-targeting versus ion-channel/calcium-targeting - is mechanistically
matched to a given carrier's genotype.
evidence:
- reference: PMID:28735292
reference_title: "Pathogenesis of Hypertrophic Cardiomyopathy is Mutation Rather Than Disease Specific: A Comparison of the Cardiac Troponin T E163R and R92Q Mouse Models."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In R92Q myocardium, we found a blunted response to inotropic
interventions, slower decay of Ca2+ transients, reduced SERCA function,
and increased Ca2+/calmodulin kinase II activity. Contrarily, secondary
alterations of E-C coupling and signaling were minimal in E163R
myocardium.
explanation: >-
States the divergence explicitly: the R92Q model is dominated by
excitation-contraction coupling remodeling while the E163R model is
dominated by primary myofilament energetic abnormalities, both producing
the shared HCM phenotype by different molecular routes.
- reference: PMID:11600691
reference_title: "Cardiac troponin T mutations: correlation between the type of mutation and the nature of myofilament dysfunction in transgenic mice."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Our data indicate that an important mutation-linked effect on cardiac
function is the result of an inefficient use of ATP at the myofilament
level. Furthermore, the extent of the mutation-induced dysfunction
depends not only on the nature of the mutation, but also on the
concentration of the mutant protein in the sarcomere.
explanation: >-
Independent transgenic-mouse evidence that both which TNNT2 mutation is
present and how much mutant protein is expressed determine the nature
and severity of myofilament dysfunction. PARTIAL because it documents
dose- and mutation-dependence in general rather than the specific
myofilament/E-C-coupling divergence claimed by the R92Q/E163R
comparison.
pathophysiology:
- name: Cardiac Troponin T Thin Filament Regulatory Defect
conforms_to: "cardiomyopathy_maladaptive_remodeling#Primary Cardiomyocyte Insult"
biological_scale: MOLECULAR
role: trigger
description: >-
TNNT2 encodes cardiac troponin T, which anchors the troponin complex to
tropomyosin on the thin filament and couples calcium binding by troponin C
to the azimuthal movement of tropomyosin that exposes or occludes the
myosin-binding sites on actin. Disease-associated TNNT2 missense variants
concentrate in the tropomyosin-binding region, most classically Arg92Gln
and Arg92Trp, and act as dominant poison peptides that are incorporated
into the thin filament - even at low mutant fraction - rather than acting
through simple loss of protein. This is the primary cardiomyocyte insult of
CMH2.
genes:
- preferred_term: TNNT2
term:
id: hgnc:11949
label: TNNT2
molecular_functions:
- preferred_term: tropomyosin binding
term:
id: GO:0005523
label: tropomyosin binding
modifier: ABNORMAL
- preferred_term: structural constituent of muscle
term:
id: GO:0008307
label: structural constituent of muscle
modifier: ABNORMAL
cell_types:
- preferred_term: Cardiomyocyte
term:
id: CL:0000746
label: cardiac muscle cell
locations:
- preferred_term: Myocardium
term:
id: UBERON:0002349
label: myocardium
cellular_components:
- preferred_term: sarcomere
term:
id: GO:0030017
label: sarcomere
- preferred_term: thin filament
term:
id: GO:0005865
label: striated muscle thin filament
biological_processes:
- preferred_term: Regulation of muscle contraction
term:
id: GO:0006937
label: regulation of muscle contraction
modifier: ABNORMAL
evidence:
- reference: PMID:8205619
reference_title: "Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Missense mutations (Ile79Asn; Arg92Gln) and a mutation in the splice
donor sequence of intron 15 of the cardiac troponin T gene are also
shown to cause FHC.
explanation: >-
The founding CMH2 observation: cardiac troponin T missense variants
cause familial hypertrophic cardiomyopathy, in the same study that
established the founding CMH3 (TPM1) variants.
- reference: PMID:8205619
reference_title: "Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Because alpha-tropomyosin and cardiac troponin T as well as beta myosin
heavy chain mutations cause the same phenotype, we conclude that FHC is
a disease of the sarcomere.
explanation: >-
Establishes that the TNNT2 lesion belongs to the same sarcomeric-protein
class as the thick- and thin-filament regulatory causes of HCM.
- reference: PMID:37159677
reference_title: Low expression of the K280N TNNT2 mutation is sufficient to increase basal myofilament activation in human hypertrophy cardiomyopathy.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
A low level (14%) of cTnT-K280N mutation elevated Ca2+-sensitivity.
explanation: >-
Human explanted-cardiomyocyte troponin-exchange evidence that the mutant
TNNT2 peptide need only occupy a small fraction of the thin filament to
perturb regulatory function, characteristic of a dominant poison-peptide
mechanism rather than simple haploinsufficiency.
downstream:
- target: Increased Myofilament Calcium Sensitivity and Loss of PKA-Mediated Desensitization
causal_link_type: DIRECT
hypothesis_groups:
- tnnt2_calcium_sensitization_uncoupling
- name: Increased Myofilament Calcium Sensitivity and Loss of PKA-Mediated Desensitization
biological_scale: MOLECULAR
role: amplifier
description: >-
Mutant cardiac troponin T shifts the thin filament toward the calcium-bound,
open regulatory state at lower calcium concentrations than wild type,
raising myofilament calcium sensitivity - a consistent finding across the
TNNT2 HCM alleles studied by in vitro motility, skinned-fibre, and
hiPSC-cardiomyocyte assays. A second, mutation-recurring abnormality is
uncoupling of calcium sensitivity from troponin I phosphorylation by
protein kinase A, which normally lowers calcium sensitivity as part of the
beta-adrenergic lusitropic response; several TNNT2 mutant troponins are
unresponsive to this modulation, removing the physiological
desensitization reserve.
cell_types:
- preferred_term: Cardiomyocyte
term:
id: CL:0000746
label: cardiac muscle cell
molecular_functions:
- preferred_term: calcium ion binding
term:
id: GO:0005509
label: calcium ion binding
modifier: INCREASED
biological_processes:
- preferred_term: Regulation of the force of heart contraction
term:
id: GO:0002026
label: regulation of the force of heart contraction
modifier: ABNORMAL
evidence:
- reference: PMID:27036851
reference_title: Mutations in troponin T associated with Hypertrophic Cardiomyopathy increase Ca(2+)-sensitivity and suppress the modulation of Ca(2+)-sensitivity by troponin I phosphorylation.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Five TnT mutations (Δ14, Δ28 + 7, ΔE160, S179F and K273E) studied in
recombinant troponin increased Ca(2+)-sensitivity and were all fully
uncoupled.
explanation: >-
Systematic in vitro survey of seven HCM-causing TNNT2 mutations showing
calcium sensitization plus uncoupling as the consistent molecular
signature.
- reference: PMID:11600691
reference_title: "Cardiac troponin T mutations: correlation between the type of mutation and the nature of myofilament dysfunction in transgenic mice."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Normalized pCa-tension relationships of R92Q and cTnT(DEL) fibres
demonstrated a significant increase in sensitivity to Ca2+ at short (2.0
microm) and long (2.3 microm) sarcomere lengths (SL).
explanation: >-
Direct skinned-fibre measurement of increased calcium sensitivity in
transgenic R92Q myocardium at physiological sarcomere lengths.
- reference: PMID:37159677
reference_title: Low expression of the K280N TNNT2 mutation is sufficient to increase basal myofilament activation in human hypertrophy cardiomyopathy.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
cTnT-K280N hiPSC-CMs show elevated diastolic Ca2+ and increases in cell
shortening. Impaired cardiomyocyte relaxation was only evident in
homozygous cTnT-K280N hiPSC-CMs.
explanation: >-
Extends the calcium-sensitization mechanism to isogenic CRISPR-edited
human iPSC-cardiomyocytes, connecting it to elevated diastolic calcium
and impaired relaxation.
downstream:
- target: Cardiomyocyte Hypercontractility and Energetic Inefficiency
causal_link_type: DIRECT
- target: Beat-to-Beat Calcium and Electrophysiological Instability
causal_link_type: DIRECT
description: >-
A parallel branch, independent of the structural hypertrophy pathway,
by which the same calcium-sensitized thin filament directly destabilizes
cardiomyocyte electrophysiology.
- name: Beat-to-Beat Calcium and Electrophysiological Instability
biological_scale: CELLULAR
role: amplifier
description: >-
Because the calcium-sensitized thin filament buffers cytosolic calcium
more avidly, the beat-to-beat cytosolic calcium transient is reduced and
its decay altered, which destabilizes cardiomyocyte electrophysiology
independent of any structural change. In human CRISPR-edited I79N hiPSC
cardiomyocytes and in transgenic I79N/F110I/R278C mouse hearts, this
manifests as beat-to-beat instability, action potential triangulation, and
- at increasing pacing frequency - alternans of both membrane voltage and
calcium transients, together with increased dispersion of ventricular
conduction velocity. This electrophysiological branch is the direct
mechanistic link between the calcium-handling lesion and the malignant
arrhythmic phenotype, distinct from and largely independent of the degree
of structural hypertrophy.
cell_types:
- preferred_term: Cardiomyocyte
term:
id: CL:0000746
label: cardiac muscle cell
biological_processes:
- preferred_term: Cardiac muscle cell action potential
term:
id: GO:0086001
label: cardiac muscle cell action potential
modifier: ABNORMAL
- preferred_term: Regulation of cytosolic calcium ion concentration
term:
id: GO:0051480
label: regulation of cytosolic calcium ion concentration
modifier: ABNORMAL
evidence:
- reference: PMID:34977031
reference_title: "Mechanisms of Arrhythmogenicity of Hypertrophic Cardiomyopathy-Associated Troponin T (TNNT2) Variant I79N."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
These changes in Ca2+ handling resulted in beat-to-beat instability and
triangulation of the cardiac action potential, which are predictors of
arrhythmia risk.
explanation: >-
Human CRISPR-edited I79N hiPSC-cardiomyocyte evidence directly linking
the TNNT2-mutant calcium-handling defect to an electrophysiological
arrhythmia substrate.
- reference: PMID:34977031
reference_title: "Mechanisms of Arrhythmogenicity of Hypertrophic Cardiomyopathy-Associated Troponin T (TNNT2) Variant I79N."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
While wild-type (WT) hiPSC-CMs were accurately entrained to frequencies
of at least 150 bpm, the I79N hiPSC-CMs demonstrated clear patterns of
alternans for both V m and Ca2+ transients at frequencies >75 bpm.
explanation: >-
Quantifies the rate-dependent electrophysiological instability
(alternans) that emerges in I79N mutant cardiomyocytes well below the
pacing rate tolerated by isogenic controls.
- reference: PMID:34977031
reference_title: "Mechanisms of Arrhythmogenicity of Hypertrophic Cardiomyopathy-Associated Troponin T (TNNT2) Variant I79N."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Mice expressing the I79N variant were particularly susceptible to
ventricular tachycardia and arrhythmias that was coincident with an
increased myofibrillar Ca2+ sensitivity, action potential triangulation,
and increased dispersion of ventricular conduction velocities at fast
heart rates in the absence of structural abnormalities.
explanation: >-
Corroborates the electrophysiological mechanism in transgenic mice
studied prior to any overt hypertrophy developing, establishing that
the arrhythmic substrate is not downstream of, and can precede,
structural remodeling.
downstream:
- target: Malignant Arrhythmogenic Substrate Despite Mild Hypertrophy
causal_link_type: DIRECT
- name: Cardiomyocyte Hypercontractility and Energetic Inefficiency
biological_scale: CELLULAR
role: effector
description: >-
The calcium-sensitized, uncoupled thin filament produces cardiomyocyte
hypercontractility with a disproportionate rise in the energetic cost of
tension generation: mutant fibres develop increased force per unit calcium
but consume ATP inefficiently relative to the tension produced, and the
magnitude of this energetic penalty scales with the fraction of mutant
protein incorporated into the sarcomere. Downstream, mutation-specific
secondary changes in excitation-contraction coupling (blunted inotropic
reserve, slowed calcium-transient decay, altered SERCA function and
CaMKII activity for the R92Q allele) compound the primary myofilament
lesion, so cellular dysfunction in CMH2 is not attributable to the
thin-filament defect alone.
cell_types:
- preferred_term: Cardiomyocyte
term:
id: CL:0000746
label: cardiac muscle cell
biological_processes:
- preferred_term: Muscle contraction
term:
id: GO:0006936
label: muscle contraction
modifier: INCREASED
- preferred_term: ATP metabolic process
term:
id: GO:0046034
label: ATP metabolic process
modifier: ABNORMAL
evidence:
- reference: PMID:11600691
reference_title: "Cardiac troponin T mutations: correlation between the type of mutation and the nature of myofilament dysfunction in transgenic mice."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
At short SL, Ca2+-activated maximal tension in both R92Q and cTnT(DEL)
fibres decreased significantly (24 and 21 %, respectively; P < 0.005),
with no corresponding decrease in Ca2+-activated maximal ATPase
activity. Therefore, at short SL, the tension cost in R92Q and
cTnT(DEL) fibres increased by 35 and 29 %, respectively (P < 0.001).
explanation: >-
Quantifies the energetic inefficiency directly: ATP turnover is
maintained while force generation falls, raising the tension cost of
contraction in both TNNT2 mutant fibre types studied.
- reference: PMID:28735292
reference_title: "Pathogenesis of Hypertrophic Cardiomyopathy is Mutation Rather Than Disease Specific: A Comparison of the Cardiac Troponin T E163R and R92Q Mouse Models."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Echocardiography showed left ventricular hypertrophy, enhanced
contractility, and diastolic dysfunction in both models; however, these
phenotypes were more pronounced in the R92Q mice.
explanation: >-
Documents enhanced (hypercontractile) function and diastolic
dysfunction in both TNNT2 mouse models, with the R92Q allele showing the
more severe phenotype.
- reference: PMID:37159677
reference_title: Low expression of the K280N TNNT2 mutation is sufficient to increase basal myofilament activation in human hypertrophy cardiomyopathy.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
The cTnT-K280N mutation increases myofilament Ca2+-sensitivity,
elevates diastolic Ca2+, enhances contractility and impairs cellular
relaxation.
explanation: >-
Human patient-derived and isogenic hiPSC-cardiomyocyte confirmation that
the calcium-sensitized thin filament produces cellular hypercontractility
with impaired relaxation.
downstream:
- target: Cardiomyocyte Hypertrophy with Disarray and Fibrosis, Often Disproportionately Mild
causal_link_type: DIRECT
- name: Cardiomyocyte Hypertrophy with Disarray and Fibrosis, Often Disproportionately Mild
conforms_to: "cardiomyopathy_maladaptive_remodeling#Ventricular Remodeling"
biological_scale: TISSUE
role: central_effector
description: >-
Chronic myofilament hypercontractility and calcium-dependent hypertrophic
signaling drive cardiomyocyte hypertrophy, myofiber disarray, and
interstitial fibrosis, the histological substrate common to hypertrophic
cardiomyopathy generally. The distinguishing feature of CMH2 is that this
remodeling is frequently mild or subclinical on echocardiography relative
to carriers of MYH7 variants, even though the underlying myofilament
defect and downstream arrhythmic risk are severe - the wall-thickness
measurement systematically understates disease severity for many TNNT2
alleles.
cell_types:
- preferred_term: Cardiomyocyte
term:
id: CL:0000746
label: cardiac muscle cell
- preferred_term: Cardiac Fibroblast
term:
id: CL:0002548
label: fibroblast of cardiac tissue
locations:
- preferred_term: left ventricle
term:
id: UBERON:0002084
label: heart left ventricle
- preferred_term: interventricular septum
term:
id: UBERON:0002094
label: interventricular septum
biological_processes:
- preferred_term: Cardiac muscle hypertrophy in response to stress
term:
id: GO:0014898
label: cardiac muscle hypertrophy in response to stress
modifier: INCREASED
- preferred_term: Extracellular matrix organization
term:
id: GO:0030198
label: extracellular matrix organization
modifier: INCREASED
evidence:
- reference: PMID:7898523
reference_title: Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The mean (+/- SD) maximal thickness of the left ventricular wall in
subjects with cardiac troponin T mutations (16.7 +/- 5.5 mm) was
significantly less than that in subjects with beta cardiac myosin
heavy-chain mutations (23.7 +/- 7.7 mm, P < 0.001).
explanation: >-
Directly quantifies the milder hypertrophy in TNNT2 mutation carriers
compared with MYH7 mutation carriers in the same cohort.
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
maximal ventricular wall thickness 11.3 +/- 5.4 mm) and low disease
penetrance by clinical criteria (40% by echocardiography)
explanation: >-
Independent pedigree confirmation of minimal hypertrophy on
echocardiography in gene carriers of the Arg92Trp allele.
downstream:
- target: Malignant Arrhythmogenic Substrate Despite Mild Hypertrophy
causal_link_type: DIRECT
- target: Diastolic Dysfunction
causal_link_type: DIRECT
- name: Malignant Arrhythmogenic Substrate Despite Mild Hypertrophy
biological_scale: ORGANISM
role: consequence
description: >-
The clinical hallmark of CMH2, first described for the Arg92 hotspot and
confirmed in independent pedigrees, is a dissociation between the degree
of left ventricular hypertrophy and the risk of sudden cardiac death:
carriers of malignant TNNT2 alleles have a high incidence of sudden death,
often at a young age, despite mild or even subclinical hypertrophy on
imaging. This "malignant but mild" pattern means that wall-thickness-based
risk stratification alone systematically underestimates risk for these
carriers, and it is why genetic testing and genotype-specific counselling
are emphasized for TNNT2 families. The pattern is allele-dependent rather
than gene-wide: the founder variant p.Asn271Ile instead produces late-onset,
low-risk disease, so risk assessment must be made at the level of the
specific variant.
evidence:
- reference: PMID:7898523
reference_title: Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These mutations are characterized by relatively mild and sometimes
subclinical hypertrophy but a high incidence of sudden death.
explanation: >-
States the defining dissociation between mild hypertrophy and high
sudden-death risk for TNNT2 mutations directly.
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These data support the observation that apparently diverse cardiac
troponin T gene mutations produce a consistent disease phenotype.
Because this is one of poor prognosis, despite deceptively mild or
undetectable hypertrophy, genotyping at this locus may be particularly
informative in patient management and counselling.
explanation: >-
Independent pedigree study confirming the malignant-but-mild phenotype
across multiple distinct troponin T alleles, and explicitly recommending
genotype-based counselling as a result.
- reference: PMID:40310325
reference_title: The p.Asn271Ile Variant in the TNNT2 Gene Is Associated With Low-Risk Late-Onset Hypertrophic Cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Variant-specific rather than gene-specific prognosis should be
considered during sudden cardiac death risk assessment.
explanation: >-
PARTIAL because this variant is the counter-example rather than a
confirmation of the malignant pattern: it establishes that the
malignant-but-mild phenotype is a property of specific TNNT2 alleles
(codon 92 hotspot) and not of the gene as a whole.
downstream:
- target: Progressive Heart Failure
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
A minority of carriers who survive without a sudden arrhythmic event
progress to structural heart failure through the same remodeling
pathway shared with hypertrophic cardiomyopathy generally.
- name: Diastolic Dysfunction
conforms_to: "cardiomyopathy_maladaptive_remodeling#Progressive Contractile Dysfunction"
biological_scale: ORGANISM
role: effector
description: >-
Impaired relaxation from the calcium-sensitized, hypercontractile
myofilament and (in the R92Q-type allelic branch) secondary alterations in
calcium-transient decay together produce diastolic dysfunction, with
prolonged twitch relaxation demonstrated directly in TNNT2 mutant mouse
myocardium and trabeculae and impaired relaxation seen in human
TNNT2-mutant cardiomyocytes.
cell_types:
- preferred_term: Cardiomyocyte
term:
id: CL:0000746
label: cardiac muscle cell
evidence:
- reference: PMID:28735292
reference_title: "Pathogenesis of Hypertrophic Cardiomyopathy is Mutation Rather Than Disease Specific: A Comparison of the Cardiac Troponin T E163R and R92Q Mouse Models."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Both E163R and R92Q trabeculae showed prolonged twitch relaxation and
increased occurrence of premature beats.
explanation: >-
Direct physiological measurement of prolonged relaxation and increased
ectopy in trabeculae from both TNNT2 mouse models.
- reference: PMID:37159677
reference_title: Low expression of the K280N TNNT2 mutation is sufficient to increase basal myofilament activation in human hypertrophy cardiomyopathy.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Impaired cardiomyocyte relaxation was only evident in homozygous
cTnT-K280N hiPSC-CMs.
explanation: >-
Human iPSC-cardiomyocyte confirmation of impaired relaxation, with a
gene-dose relationship (homozygous but not heterozygous mutant cells
showing the impairment) that maps to the diastolic-dysfunction node.
downstream:
- target: Progressive Heart Failure
causal_link_type: DIRECT
- name: Progressive Heart Failure
conforms_to: "cardiomyopathy_maladaptive_remodeling#Structural Cardiac Impairment and Heart Failure"
biological_scale: ORGANISM
role: consequence
description: >-
In carriers who do not experience a sudden arrhythmic event, sustained
hypercontractility, diastolic dysfunction, and interstitial fibrosis
progress over years to structural cardiac impairment and congestive heart
failure, following the same generic maladaptive-remodeling trajectory
shared with hypertrophic cardiomyopathy generally and detailed on the
umbrella Hypertrophic Cardiomyopathy entry.
evidence:
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A previous report suggested that mutations in the cardiac troponin T
gene were notable because they were associated with a particularly poor
prognosis but only mild hypertrophy.
explanation: >-
Establishes the poor overall prognosis associated with TNNT2 mutations,
of which the minority progressing to heart failure (rather than sudden
death) is a component.
- reference: PMID:22752727
reference_title: "The role of TWEAK/Fn14 in cardiac remodeling."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The pathophysiological basis of heart failure is cardiac remodeling, a
process that comprises structural and functional changes including
cardiomyocyte proliferation, hypertrophy, necrosis, apoptosis,
autophagy, interstitial fibrosis, contractile dysfunction and
ventricular dilatation.
explanation: >-
Anchors the consequence node to the generic cardiomyopathy remodeling
pathway shared with the cardiomyopathy_maladaptive_remodeling module.
Evidence source is OTHER because this is a mechanistic review.
phenotypes:
- name: Hypertrophic Cardiomyopathy
description: >-
The defining phenotype of CMH2: unexplained left ventricular hypertrophy,
which is frequently only mild or subclinical relative to the underlying
disease severity in carriers of malignant TNNT2 alleles.
phenotype_term:
preferred_term: Hypertrophic cardiomyopathy
term:
id: HP:0001639
label: Hypertrophic cardiomyopathy
evidence:
- reference: PMID:8205619
reference_title: "Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Missense mutations (Ile79Asn; Arg92Gln) and a mutation in the splice
donor sequence of intron 15 of the cardiac troponin T gene are also
shown to cause FHC.
explanation: >-
Founding demonstration that TNNT2 missense mutations cause familial
hypertrophic cardiomyopathy.
- name: Left Ventricular Hypertrophy, Often Mild
description: >-
Increased left ventricular wall thickness that, in carriers of malignant
TNNT2 alleles such as the codon-92 hotspot, is frequently only mildly or
subclinically increased compared with carriers of MYH7 mutations, even
though downstream arrhythmic risk is high.
phenotype_term:
preferred_term: Left ventricular hypertrophy
term:
id: HP:0001712
label: Left ventricular hypertrophy
frequency: FREQUENT
evidence:
- reference: PMID:7898523
reference_title: Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The mean (+/- SD) maximal thickness of the left ventricular wall in
subjects with cardiac troponin T mutations (16.7 +/- 5.5 mm) was
significantly less than that in subjects with beta cardiac myosin
heavy-chain mutations (23.7 +/- 7.7 mm, P < 0.001).
explanation: >-
Quantifies left ventricular hypertrophy in TNNT2 carriers and its
relative mildness compared with MYH7 carriers. FREQUENT is used for the
presence of hypertrophy itself (documented across cohorts), while its
characteristic mildness is captured in the description and the
pathophysiology node rather than as a separate frequency claim.
- name: Myocardial Fibrosis
description: >-
Interstitial and replacement fibrosis of the myocardium, part of the
generic maladaptive remodeling response shared with hypertrophic
cardiomyopathy generally.
phenotype_term:
preferred_term: Myocardial fibrosis
term:
id: HP:0001685
label: Myocardial fibrosis
evidence:
- reference: PMID:22752727
reference_title: "The role of TWEAK/Fn14 in cardiac remodeling."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The pathophysiological basis of heart failure is cardiac remodeling, a
process that comprises structural and functional changes including
cardiomyocyte proliferation, hypertrophy, necrosis, apoptosis,
autophagy, interstitial fibrosis, contractile dysfunction and
ventricular dilatation.
explanation: >-
Establishes interstitial fibrosis as a conserved component of the
cardiomyopathy remodeling process that CMH2 shares with other genetic
causes of hypertrophic cardiomyopathy. Evidence source is OTHER because
this is a mechanistic review.
- name: Left Ventricular Diastolic Dysfunction
description: >-
Impaired ventricular relaxation and filling, demonstrated directly in
TNNT2 mutant mouse myocardium and human TNNT2-mutant cardiomyocytes.
phenotype_term:
preferred_term: Left ventricular diastolic dysfunction
term:
id: HP:0025168
label: Left ventricular diastolic dysfunction
evidence:
- reference: PMID:28735292
reference_title: "Pathogenesis of Hypertrophic Cardiomyopathy is Mutation Rather Than Disease Specific: A Comparison of the Cardiac Troponin T E163R and R92Q Mouse Models."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Echocardiography showed left ventricular hypertrophy, enhanced
contractility, and diastolic dysfunction in both models
explanation: >-
Echocardiographic demonstration of diastolic dysfunction in both TNNT2
mouse models studied.
- name: Ventricular Arrhythmia
description: >-
Malignant ventricular arrhythmia - the clinical event that the
arrhythmogenic substrate produces and that precedes sudden cardiac death
in CMH2. Its burden is strongly variant-dependent within TNNT2: it is the
dominant component of the adverse-outcome endpoint in the low-risk
p.Asn271Ile founder cohort and is far more frequent in codon-92 carriers.
phenotype_term:
preferred_term: Ventricular arrhythmia
term:
id: HP:0004308
label: Ventricular arrhythmia
evidence:
- reference: PMID:40310325
reference_title: The p.Asn271Ile Variant in the TNNT2 Gene Is Associated With Low-Risk Late-Onset Hypertrophic Cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
only 4.2% of patients reached the primary endpoint (3.2% malignant
ventricular arrhythmia, 1.1% end-stage heart failure). Codon 92
variants' carriers (76 individuals, 28 probands) had a higher
penetrance, being diagnosed 19.4 years earlier, and they exhibited a
significantly worse prognosis (primary endpoint in 34.3%; P < 0.001).
explanation: >-
Direct human documentation of malignant ventricular arrhythmia as an
observed outcome in TNNT2 carriers, and of its variant-dependence. No
`frequency:` is asserted because the two rates quoted here are not
comparable bands: 3.2% is the isolated arrhythmia rate in the low-risk
p.Asn271Ile cohort, while 34.3% is a composite endpoint that also
includes end-stage heart failure.
- reference: PMID:34977031
reference_title: "Mechanisms of Arrhythmogenicity of Hypertrophic Cardiomyopathy-Associated Troponin T (TNNT2) Variant I79N."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Mice expressing the I79N variant were particularly susceptible to
ventricular tachycardia and arrhythmias that was coincident with an
increased myofibrillar Ca2+ sensitivity, action potential triangulation,
and increased dispersion of ventricular conduction velocities at fast
heart rates in the absence of structural abnormalities
explanation: >-
Model-organism corroboration that the arrhythmia arises from the
calcium-sensitization and repolarization-instability mechanism curated
upstream, and that it does so in the absence of structural
abnormality - the defining CMH2 dissociation of arrhythmic risk from
degree of hypertrophy. Supporting, not sole, evidence for this human
phenotype.
- name: Sudden Cardiac Death
description: >-
Sudden, presumed arrhythmic death, disproportionately frequent relative to
the degree of hypertrophy for carriers of malignant TNNT2 alleles such as
the codon-92 hotspot, and the clinical feature that most distinguishes
CMH2 from milder-risk sarcomeric HCM entities.
phenotype_term:
preferred_term: Sudden cardiac death
term:
id: HP:0001645
label: Sudden cardiac death
frequency: FREQUENT
evidence:
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
... a high incidence of sudden cardiac death (mean age 17 +/- 9 years).
explanation: >-
Documents a high incidence of sudden cardiac death at a young mean age
in TNNT2 mutation carriers. FREQUENT reflects the qualitative language
("high incidence") used across the founding cohort studies for the
malignant alleles that are the focus of this entry; it is not a claim
about penetrance across every TNNT2 allele (see the p.Asn271Ile
counter-example under genetic case_fractions/downstream nodes).
- name: Congestive Heart Failure
description: >-
Progressive heart failure in carriers who do not experience a sudden
arrhythmic event, following the generic cardiomyopathy remodeling
trajectory shared with hypertrophic cardiomyopathy generally.
phenotype_term:
preferred_term: Congestive heart failure
term:
id: HP:0001635
label: Congestive heart failure
evidence:
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A previous report suggested that mutations in the cardiac troponin T
gene were notable because they were associated with a particularly poor
prognosis but only mild hypertrophy.
explanation: >-
Documents the poor overall prognosis of TNNT2 mutation carriers, of
which progression to heart failure is a component alongside sudden
death.
diagnosis:
- name: Genotype-Informed Risk Stratification and Cascade Genetic Testing
description: >-
Because the malignant TNNT2 alleles that define CMH2 can produce a high
risk of sudden cardiac death despite mild or subclinical hypertrophy,
wall-thickness-based risk stratification alone is insufficient for these
families; genetic testing to establish TNNT2 genotype, and cascade testing
of relatives, is emphasized for management and counselling. Risk
assessment must additionally be made at the level of the specific variant,
since not every TNNT2 allele (for example the low-risk founder variant
p.Asn271Ile) carries the malignant phenotype. General hypertrophic
cardiomyopathy management - beta-blockers, mavacamten and other cardiac
myosin inhibitors, ICD implantation for high-risk carriers, and septal
reduction therapy for outflow obstruction - is curated on the umbrella
Hypertrophic Cardiomyopathy entry and is not duplicated here.
diagnosis_term:
preferred_term: Genetic Testing
term:
id: NCIT:C15709
label: Genetic Testing
results: Identifies a pathogenic TNNT2 variant and its specific allele
evidence:
- reference: PMID:7898523
reference_title: Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These mutations are characterized by relatively mild and sometimes
subclinical hypertrophy but a high incidence of sudden death. Genetic
testing may therefore be especially important in this group.
explanation: >-
States directly that genetic testing is especially valuable for TNNT2
carriers because clinical (wall-thickness) risk markers understate the
true risk.
- reference: PMID:9060892
reference_title: Sudden death due to troponin T mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Because this is one of poor prognosis, despite deceptively mild or
undetectable hypertrophy, genotyping at this locus may be particularly
informative in patient management and counselling.
explanation: >-
Independent recommendation that genotyping at the TNNT2 locus is
particularly informative for management and counselling, corroborating
the rationale for genotype-informed rather than imaging-only risk
assessment.
- reference: PMID:40310325
reference_title: The p.Asn271Ile Variant in the TNNT2 Gene Is Associated With Low-Risk Late-Onset Hypertrophic Cardiomyopathy.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Variant-specific rather than gene-specific prognosis should be
considered during sudden cardiac death risk assessment.
explanation: >-
Supports the variant-level (not gene-level) granularity required for
TNNT2 risk counselling, since a low-risk founder variant coexists with
the malignant codon-92 hotspot within the same gene.
notes: >-
Curated under `diagnosis:` rather than `treatments:` - it is a diagnostic
and risk-stratification procedure, not a therapy. The entry carries no
`treatments:` section by design: every therapeutic option for CMH2
(beta-blockers, cardiac myosin inhibitors, ICD, septal reduction) is
cross-gene HCM management curated on the umbrella entry, and duplicating
it per gene was a deliberate lumping call (see the scope note below).
The wider diagnostic workup - echocardiographic and CMR wall-thickness
criteria, late gadolinium enhancement, ECG and ambulatory monitoring - is
not modeled here because neither cached reference that would source it is
minable: PMID:38718139 caches as an abstract-only AIM/METHODS/STRUCTURE
stub with no criteria in it, and the GeneReviews chapter PMID:20301725
caches as its purpose statement alone. Adding those procedures would
require citations not currently in this PR's reference cache.
references:
- reference: PMID:20301725
title: "Nonsyndromic Hypertrophic Cardiomyopathy Overview"
tags:
- GeneReviews
- reference: PMID:38718139
title: "2024 AHA/ACC/AMSSM/HRS/PACES/SCMR Guideline for the Management of Hypertrophic Cardiomyopathy: A Report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines."
notes: >-
Scope note: this entry is the TNNT2 gene-specific entity (MONDO:0007266), not
the HCM umbrella. The umbrella entry Hypertrophic_Cardiomyopathy
(MONDO:0005045) carries the cross-gene phenotype and treatment picture
(mavacamten, beta-blockers, ICD implantation, septal reduction therapy);
content here is deliberately restricted to what is specific to TNNT2
thin-filament biology and to the malignant-but-mild genotype-phenotype pattern
that most distinguishes CMH2 from the other numbered CMH entries.
ClinGen classification note: the TNNT2-hypertrophic cardiomyopathy
gene-disease validity assertion
(CGGV:assertion_ef922dc4-4e41-422b-ac3d-605fea375005-2021-02-04T050000.000Z)
is classified Moderate under the older
SOP7 framework (2021), in contrast to the Definitive classifications now
recorded for MYH7, MYBPC3, and TPM1 under SOP9. This is a curation-vintage
artifact, not a statement that TNNT2 causality is weaker than the founding
1994 discovery and the extensive subsequent genotype-phenotype literature
would suggest; it is recorded here rather than silently upgraded.
Named Entity Confusion (NEC) preflight: the CMH numbered series is a
documented high-NEC-risk class (numbered disease-by-gene series). The
requested falcon (Edison) deep-research provider was run
(research/Hypertrophic_Cardiomyopathy_2-deep-research-falcon.md, reference
validation: 11/11 references resolved, 0 confabulated) and
`just preflight-dr research/Hypertrophic_Cardiomyopathy_2-deep-research-falcon.md
MONDO:0007266` was run before any of its content was used for curation.
Automated verdict was SKIP (MONDO:0007266 records no RO:0004003 causal-gene
relationship for the automated gene-identity check to key on, even though the
earlier `runoak ... -O obo` lookup used to source this entry's disease_term
does show that relationship), so the manual fallback in the SOP was applied:
gene check - TNNT2 dominates the report's gene mentions (89 occurrences versus
4 each for NPPA/NPPB, the next most frequent); OMIM check - the report's
cited OMIM (115195) matches the MONDO xref exactly; synonym check - the
report's own framing statement explicitly disambiguates CMH2/TNNT2 from other
TNNT2-associated phenotypes (dilated cardiomyopathy, left ventricular
noncompaction) rather than conflating them. All three checks passed, so the
report was used as a lead-generation source. Three PMIDs it surfaced were
independently verified and incorporated: PMID:37929589 (a larger,
contemporary penetrance meta-analysis corroborating PMID:32731933),
PMID:34977031 (human iPSC-cardiomyocyte and transgenic-mouse evidence for the
electrophysiological arrhythmia mechanism, added as its own pathophysiology
node), and the report's TNNT2 case-fraction and hotspot-variant framing, which
matched what independent PubMed search had already produced. All PMIDs cited
in this entry - both those the report surfaced and those found independently
via PubMed search - were fetched with `just fetch-reference` and every
snippet was verified against the cached abstract; none were taken from the
report's own quotes without independent re-verification against the primary
source.
Unsourced/limited-evidence items intentionally omitted: no population-based
prevalence for the TNNT2-specific entity exists, so prevalence is recorded
as NOT_YET_DOCUMENTED rather than estimated. The 2024 AHA/ACC guideline
(PMID:38718139) is carried in the top-level references for provenance but is
deliberately not mined for an evidence snippet, because its cached PubMed
record contains only AIM/METHODS/STRUCTURE sections with no quotable
clinical recommendation text - the same limitation noted on the sibling
Hypertrophic_Cardiomyopathy_4 entry. Mavacamten and other genotype-agnostic
HCM pharmacotherapy are left to the umbrella entry rather than duplicated
here without TNNT2-specific mechanistic evidence.
Hypertrophic cardiomyopathy 2 (HCM2) is the historical gene-numbered form of familial hypertrophic cardiomyopathy caused by heterozygous pathogenic variants in TNNT2, encoding cardiac troponin T. It should not be confused with generic hypertrophic cardiomyopathy (HCM), nor with other TNNT2-associated phenotypes such as dilated cardiomyopathy or left-ventricular noncompaction. Open Targets supports a literature-backed association between TNNT2 (ENSG00000118194) and HCM/familial HCM, including primary reports indexed by PMIDs 8989109, 10525521, 12707239, 27532257, 28369730, and 30681346. (OpenTargets Search: hypertrophic cardiomyopathy-TNNT2)
Because contemporary guidelines generally manage disease according to the HCM phenotype, rather than its historical numbered subtype, this report labels evidence as either TNNT2-specific or general-HCM extrapolation. The source base is aggregated disease-level literature rather than individual-patient EHR data.
| Domain | HCM2-specific fact | Suggested ontology IDs/terms | Evidence/qualification |
|---|---|---|---|
| Identity | Historical disease entity is Hypertrophic cardiomyopathy 2 (HCM2), a TNNT2-related familial hypertrophic cardiomyopathy subtype; use disease-level resources with caution because many current sources collapse numbered subtypes into generic HCM. | OMIM: 115195 (if using historical subtype mapping); TNNT2 / HGNC:11949; MONDO caveat: use generic hypertrophic cardiomyopathy MONDO:0005045 when subtype MONDO is not confidently established | TNNT2 is an established HCM target/disease association; numbering/scope caveat because recent resources emphasize gene-defined sarcomeric HCM rather than historic subtype labels (OpenTargets Search: hypertrophic cardiomyopathy-TNNT2) |
| Synonyms | Suggested labels: TNNT2-related hypertrophic cardiomyopathy, cardiac troponin T-associated hypertrophic cardiomyopathy, familial hypertrophic cardiomyopathy due to TNNT2 | MeSH/ICD not confidently subtype-specific here; retain free-text synonyms | Modern literature usually discusses TNNT2-positive HCM rather than “HCM2” as a primary label (OpenTargets Search: hypertrophic cardiomyopathy-TNNT2, topriceanu2024metaanalysisofpenetrance pages 1-2) |
| Etiology | Primary cause is heterozygous germline pathogenic/likely pathogenic variants in TNNT2, encoding cardiac troponin T, a thin-filament sarcomeric protein | TNNT2 / HGNC:11949; sarcomere/thin filament terms as annotations | Supported by disease-target evidence and TNNT2-specific primary studies/models (OpenTargets Search: hypertrophic cardiomyopathy-TNNT2, kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25) |
| Inheritance | Typically autosomal dominant with age-dependent, incomplete penetrance and variable expressivity | HPO inheritance term may be added locally if needed; no ID asserted here | General genetic HCM evidence; applies to TNNT2-positive families, with gene-specific penetrance estimates available (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, topriceanu2024metaanalysisofpenetrance pages 1-2) |
| Penetrance / natural history | Meta-analysis estimate for TNNT2 penetrance ~60% in nonproband relatives identified by cascade screening; mean age at HCM diagnosis ~38 years; phenotypic conversion across sarcomeric HCM about 15% over ~8 years from subclinical state | Phenotype conversion / age-dependent penetrance annotations | Best recent quantitative estimate; this is family/clinical-context penetrance, not incidental population penetrance (topriceanu2024metaanalysisofpenetrance pages 1-2) |
| Variant classes | Reported pathogenic TNNT2 variants in HCM include missense and small in-frame deletion variants; notable research variants include R92Q, I79N, Δ160E | Sequence Ontology terms can be added locally (missense_variant, inframe_deletion) | Variant examples are from mechanistic/model papers; not an exhaustive clinical variant catalog (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25) |
| Core phenotype | Unexplained left ventricular hypertrophy with familial sarcomeric cardiomyopathy features | HP:0001712 Left ventricular hypertrophy | TNNT2-specific and general HCM-defining feature; subtype-specific frequency not precisely quantified in retrieved evidence (cai2020establishinganew pages 21-25, nakamura2025cardiacmyosininhibitors pages 2-4) |
| Arrhythmic phenotype | TNNT2 variants can confer high arrhythmic risk and sudden death risk, sometimes despite mild hypertrophy | HP:0001645 Arrhythmia; HP:0001680 Ventricular arrhythmia; HP:0001644 Syncope; HP:0001699 Sudden cardiac death | Strongly emphasized for TNNT2 variants, especially I79N and thin-filament HCM literature (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2) |
| Diastolic/relaxation phenotype | Relaxation impairment and diastolic dysfunction are prominent early phenotypes linked to increased myofilament Ca2+ sensitivity | HP:0005157 Abnormal left ventricular diastolic function | Directly shown in TNNT2 Δ160E and zebrafish TNNT2 models (kondo2022humaninducedpluripotentstem pages 1-2, kamel2021aheterozygousmutation pages 1-2) |
| Cellular hypertrophy | Mutant cardiomyocytes show increased cell size and hypertrophic signaling | HP:0001639 Cardiomyocyte hypertrophy if locally mapped; HP:0000822? not asserted if uncertain | Derived mainly from hESC/iPSC cardiomyocyte models; keep as experimental phenotype annotation (kondo2022humaninducedpluripotentstem pages 1-2, cai2020establishinganew pages 21-25) |
| Sarcomere disarray | TNNT2-HCM models show myofilament/myofibrillar disarray | HP:0005179 Myocardial fiber disarray (suggested if local ontology supports exact term) | Strong experimental support in TNNT2 R92Q and I79N models (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25) |
| Biomarker phenotype | Natriuretic peptide and injury biomarker elevation may occur in HCM; TNNT2 I79N model showed NPPA/NPPB upregulation | HP:0031185 Elevated circulating NT-proBNP level (general-HCM extrapolation); transcript markers NPPA/NPPB | Direct TNNT2 evidence is transcriptomic/model-based; circulating biomarker use is broader HCM extrapolation (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, nakamura2025cardiacmyosininhibitors pages 13-14, ottaviani2023revisitingdiagnosisand pages 23-24) |
| Mechanism: primary biophysical defect | Upstream mechanism is increased myofilament Ca2+ sensitivity and slower Ca2+ dissociation/off-rate from thin filament regulation | GO:0051592 response to calcium ion; GO:0006936 muscle contraction; GO:0030049 muscle filament sliding | Core TNNT2 mechanism shown for I79N, Δ160E, and R92Q models (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25) |
| Mechanism: calcium handling | Mutations drive prolonged calcium decay, intracellular Ca2+ retention/buffering abnormalities, and impaired relaxation | GO:0051480 regulation of cytosolic calcium ion concentration; GO:1903779 regulation of cardiac conduction? not asserted if uncertain | Strong TNNT2-specific model evidence (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, kamel2021aheterozygousmutation pages 1-2) |
| Mechanism: hypertrophic signaling | Downstream signaling includes NFATc1 nuclear translocation and increased CaMKIIδ / phospholamban phosphorylation | GO:0006468 protein phosphorylation; GO:0007205 protein kinase C-activating GPCR signaling? not asserted; GO:0006950 response to stress if needed | Direct TNNT2 Δ160E evidence; useful for pathway annotation but not yet routine clinical biomarker use (kondo2022humaninducedpluripotentstem pages 1-2) |
| Mechanism: electrophysiology | Ca2+ dysregulation promotes beat-to-beat instability, action-potential triangulation, and alternans, creating an arrhythmic substrate/trigger | GO:0086001 cardiac muscle cell action potential; GO:1903779 regulation of cardiac conduction | Strong TNNT2 I79N hiPSC-CM evidence (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2) |
| Mechanism: energetics / oxidative stress | Recent HCM work supports a broader sarcomeric-HCM mechanism in which increased Ca2+ sensitivity causes bioenergetic mismatch, mitochondrial ROS, spontaneous Ca2+ release, and arrhythmias | GO:0006979 response to oxidative stress; GO:0042775 mitochondrial ATP synthesis coupled electron transport | General-HCM extrapolation from HCM mouse models including TNNT2-I79N; promising but partly preprint-stage for 2024 evidence (dolder2025experimentalmodelsof pages 36-36) |
| Tissue remodeling | Fibrosis/ECM-remodeling programs are downstream disease features; TNNT2 I79N transcriptomics showed ECM-remodeling signatures | GO:0030198 extracellular matrix organization; GO:0061448 connective tissue development? not asserted; HP:0005680 Myocardial fibrosis (suggested) | Direct transcriptomic/model support; clinical fibrosis imaging is often inferred from general HCM practice (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12) |
| Cell types | Primary affected cell type is cardiomyocyte; fibroblasts and endothelial/immune compartments are likely secondary participants in remodeling/fibrosis | CL:0002494 cardiomyocyte; CL:0000057 fibroblast; endothelial cell term may be added locally if needed | Cardiomyocyte involvement is direct; fibroblast/endothelial participation is mainly general-HCM extrapolation from fibrosis literature (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, dolder2025experimentalmodelsof pages 36-36) |
| Anatomy | Primary organ/site is heart, especially left ventricular myocardium; obstruction may involve left ventricular outflow tract in obstructive phenotypes | UBERON:0000948 heart; UBERON:0002084 myocardium; UBERON:0002080 cardiac ventricle; LVOT term add locally if curated | HCM-anatomy statements are partly generic HCM criteria because TNNT2-specific anatomy is not uniquely distinct (cai2020establishinganew pages 21-25, sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12, nakamura2025cardiacmyosininhibitors pages 2-4) |
| Subcellular localization | Disease-relevant compartment is the sarcomeric thin filament / myofilament complex | GO cellular-component terms can be added locally, e.g. sarcomere/thin filament if curated from external ontology | Strong mechanistic fit, but specific GO CC IDs were not verified in retrieved context, so not asserted numerically |
| Diagnostics: clinical definition | HCM diagnosis in adults generally requires unexplained LV wall thickness ≥15 mm; ≥13 mm in first-degree relatives can support diagnosis | Diagnostic threshold annotation; HP:0001712 | General-HCM extrapolation from current diagnostic practice, applied to TNNT2-HCM when subtype-specific criteria are absent (nakamura2025cardiacmyosininhibitors pages 2-4) |
| Diagnostics: imaging | Transthoracic echocardiography is first-line; CMR is recommended for morphology clarification, apical disease, aneurysm/thrombus detection, and fibrosis/LGE assessment; provocation/exercise testing is used when obstruction is suspected but absent at rest | NCIT-style labels: Echocardiography, Cardiac MRI, Exercise Testing | Guideline-review level evidence, largely generic HCM but clinically applicable to TNNT2-HCM (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12, nakamura2025cardiacmyosininhibitors pages 2-4) |
| Diagnostics: genetic testing | Multigene cardiomyopathy testing including TNNT2 is recommended to support diagnosis, cascade screening, and phenocopy distinction | TNNT2 / HGNC:11949; NCIT-style labels: Molecular Genetic Testing, Cascade Screening | Strongly supported in guideline reviews; phenotype-negative relatives are not genetically “diagnosed” without a known familial variant (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12, nakamura2025cardiacmyosininhibitors pages 2-4) |
| Differential diagnosis | Exclude HCM phenocopies and secondary hypertrophy causes: amyloidosis, Fabry disease, glycogen storage disease, mitochondrial disease, RASopathy, valvular/loading conditions, athlete’s heart | Use generic phenocopy/differential labels locally | Mostly general-HCM evidence, important because numbered HCM subtype labels can obscure phenocopies (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12, nakamura2025cardiacmyosininhibitors pages 2-4) |
| Epidemiology | HCM prevalence broadly is about 1 in 500 in classic estimates; TNNT2-specific disease is a minority sarcomeric subset; one review/meta-analysis found TNNT2 penetrance around 60% in family screening context | Population prevalence annotation; gene-specific subset flag | General-HCM extrapolation for overall prevalence; TNNT2-specific frequency not robustly quantified in retrieved evidence (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, topriceanu2024metaanalysisofpenetrance pages 1-2) |
| Prognosis | Prognosis is variable; TNNT2 variants are notable for arrhythmia/sudden death risk and in some variants for adverse remodeling or systolic dysfunction | Sudden-death risk annotation; heart-failure progression annotation | Subtype-specific risk is variant-dependent; avoid overgeneralizing all TNNT2 variants as uniformly high risk (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2) |
| Prevention / family management | Cascade screening of relatives is central; exercise should generally be encouraged at mild-moderate intensity, while high-risk/high-intensity activity decisions are individualized; pregnancy medication review is needed and mavacamten is contraindicated in pregnancy | NCIT-style labels: Genetic Counseling, Family Screening, Exercise Counseling, Pregnancy Counseling | Mostly general-HCM guideline extrapolation but directly useful in TNNT2-HCM care pathways (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12) |
| Standard pharmacotherapy | First-line symptomatic therapy for obstructive HCM: beta-blocker; alternatives include verapamil/diltiazem; disopyramide can be added in selected obstructive cases | NCIT-style labels: Beta Adrenergic Receptor Blockade, Verapamil Therapy, Diltiazem Therapy, Disopyramide Therapy | General-HCM treatment extrapolation; no TNNT2-specific drug-response biomarker established in retrieved evidence (nakamura2025cardiacmyosininhibitors pages 11-13, nakamura2025cardiacmyosininhibitors pages 2-4) |
| Targeted therapy | Mavacamten is a cardiac myosin inhibitor for symptomatic obstructive HCM; EXPLORER-HCM primary endpoint achieved in 37% vs 17% placebo; VALOR-HCM reduced SRT eligibility to 17.9% vs 76.8% after 16 weeks | NCIT-style labels: Mavacamten Therapy, Cardiac Myosin Inhibitor Therapy | High-quality general-HCM evidence; not TNNT2-specific, but directly relevant to sarcomeric obstructive HCM clinical implementation (nakamura2025cardiacmyosininhibitors pages 13-14, nakamura2025cardiacmyosininhibitors pages 16-18, ottaviani2023revisitingdiagnosisand pages 23-24) |
| Emerging targeted therapy | Aficamten is a next-generation cardiac myosin inhibitor with shorter half-life and favorable trial results in obstructive HCM | NCIT-style labels: Aficamten Therapy, Cardiac Myosin Inhibitor Therapy | General-HCM extrapolation; regulatory/implementation status continues to evolve (nakamura2025cardiacmyosininhibitors pages 13-14, hou2025cardiacmyosininhibitors pages 12-13) |
| Procedures | If severe obstructive symptoms persist despite drug therapy, septal reduction therapy (surgical myectomy or alcohol septal ablation) is standard | NCIT-style labels: Surgical Septal Myectomy, Alcohol Septal Ablation, Septal Reduction Therapy | General-HCM standard of care; not gene-specific (nakamura2025cardiacmyosininhibitors pages 16-18, nakamura2025cardiacmyosininhibitors pages 11-13) |
| Device therapy | ICD used for primary/secondary prevention based on sudden-death risk stratification; one guideline approach recommends ICD for 5-year SCD risk ≥6% and consideration at 4–6% | NCIT-style labels: Implantable Cardioverter Defibrillator | General-HCM extrapolation from guideline review; TNNT2 genotype may inform concern but ICD decisions remain phenotype/risk-marker led (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12) |
| Advanced HF therapy | End-stage disease may require advanced heart-failure care, including transplant in rare progressed cases | NCIT-style labels: Heart Transplantation | General-HCM extrapolation; relevant because some TNNT2 variants can progress to systolic dysfunction (kondo2022humaninducedpluripotentstem pages 1-2) |
| Experimental / mechanism-based therapy | Calcium desensitization is mechanistically attractive in TNNT2-HCM; epigallocatechin-3-gallate improved calcium decay/relaxation in Δ160E iPSC-CMs | CHEBI/compound IDs not asserted here; experimental therapy label locally | Preclinical only in retrieved evidence (kondo2022humaninducedpluripotentstem pages 1-2) |
| Models: human cellular | Human hiPSC-CM and hESC-CM TNNT2 models recapitulate hypertrophy, calcium dysregulation, disarray, and pro-arrhythmic phenotypes; examples: Δ160E, I79N, R92Q | Model labels: hiPSC-derived cardiomyocyte, hESC-derived cardiomyocyte, engineered heart tissue | Strong direct disease-model evidence and useful for assay/drug screening annotation (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25) |
| Models: animal | Mouse TNNT2 models (e.g., I79N, R92Q) and zebrafish tnnt2a RK94del model reproduce Ca2+ dysregulation, remodeling, fibrosis, and arrhythmogenic traits | Organism labels locally; NCBI Taxon IDs not asserted to avoid invention | Strong comparative evidence; supports mechanism and therapeutic screening (kamel2021aheterozygousmutation pages 1-2, dolder2025experimentalmodelsof pages 36-36) |
| Data provenance | This entry should be populated primarily from aggregated disease-level resources and primary literature, not solely EHR-derived observations | Evidence-source annotation | Important because subtype identity is historical and modern datasets often aggregate into generic HCM (OpenTargets Search: hypertrophic cardiomyopathy-TNNT2, topriceanu2024metaanalysisofpenetrance pages 1-2) |
Table: This compact table summarizes key facts for Hypertrophic Cardiomyopathy 2 as TNNT2-related HCM, with ontology suggestions and evidence qualifiers for direct knowledge-base ingestion. It distinguishes TNNT2-specific findings from general-HCM extrapolations and flags uncertain identifiers to avoid over-assertion.
HCM2 is a primary sarcomeric myocardial disorder characterized by otherwise unexplained left-ventricular hypertrophy (LVH), cardiomyocyte disarray, diastolic dysfunction, and variable susceptibility to ventricular arrhythmia, heart failure, and sudden cardiac death. TNNT2 disease is notable because substantial arrhythmic risk may occur with relatively modest hypertrophy. (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25)
Identifiers and nomenclature
The causal lesion is usually a heterozygous germline TNNT2 pathogenic or likely pathogenic variant. TNNT2 is a component of the troponin complex on the sarcomeric thin filament and couples cytosolic calcium signals to actin–myosin contraction. Reported HCM-associated classes include missense substitutions and small in-frame deletions, including p.Ile79Asn (I79N), p.Arg92Gln (R92Q), and p.Glu160del (Δ160E; c.478_480del). (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25)
Risk is shaped by variant-specific biophysics, age, family history, polygenic background, sex, loading conditions, and lifestyle, but robust TNNT2-specific effect sizes are limited. The best recent synthesis concludes that penetrance is “highly variable” and influenced by still-undefined, context-dependent genetic and environmental factors. In family-based cascade screening, TNNT2 penetrance was approximately 60%, whereas penetrance of incidentally discovered sarcomeric variants in population cohorts was much lower, approximately 11% overall. (topriceanu2024metaanalysisofpenetrance pages 1-2)
Hypertension, obesity, intense adrenergic stress, dehydration, and extreme exertion can worsen the expressed HCM phenotype or provoke obstruction/arrhythmia, but they do not cause monogenic HCM2. Family history of premature sudden death is clinically important. No infectious cause is recognized.
No validated TNNT2-specific protective allele is established. Potentially protective management includes blood-pressure control, avoidance of dehydration and stimulant misuse, individualized exercise counseling, and surveillance of genotype-positive relatives. Experimental calcium desensitization improved abnormal calcium decay and relaxation in TNNT2-Δ160E cardiomyocytes, but this is not established preventive therapy. (kondo2022humaninducedpluripotentstem pages 1-2, sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12)
Clinical expression is age-dependent and highly variable, ranging from lifelong genotype-positive/phenotype-negative status to childhood or adult disease, severe arrhythmia, heart failure, or sudden death. Mean age at diagnosis among nonproband sarcomeric-variant relatives was 38 years (95% CI 36–40); this is not a TNNT2-only age estimate. (topriceanu2024metaanalysisofpenetrance pages 1-2)
Major phenotypes and suggested HPO annotations include:
Quality of life is chiefly impaired through exercise limitation, symptoms, anxiety concerning sudden death, activity restrictions, repeated surveillance, and family implications. In obstructive HCM, mavacamten improved the Kansas City Cardiomyopathy Questionnaire overall score by 14.9 versus 5.4 points with placebo; 36% achieved a ≥20-point improvement, corresponding to an NNT of approximately 5. These data are HCM-wide, not TNNT2-specific. (nakamura2025cardiacmyosininhibitors pages 13-14)
Causal gene: TNNT2 encodes cardiac troponin T, a sarcomeric thin-filament protein. Pathogenic HCM variants are predominantly heterozygous germline missense or in-frame changes and commonly exert altered-function/“poison-peptide” effects rather than simple whole-gene haploinsufficiency. Variant interpretation must follow ACMG/AMP criteria using segregation, population frequency, computational, functional, and case-enrichment evidence.
Illustrative variants include:
Pathogenic HCM alleles should generally be absent or extremely rare in gnomAD; however, no universal allele-frequency value applies. Exact ClinVar classification and gnomAD frequency must be recorded per HGVS allele and transcript. VUSs are not suitable for predictive cascade testing or irreversible management decisions.
No recurrent chromosomal abnormality, repeat expansion, mitochondrial mutation, or somatic mechanism defines HCM2. Modifier genes and polygenic background likely contribute to penetrance, but no modifier is currently sufficiently validated for routine HCM2 risk prediction. Epigenetic abnormalities are biologically plausible downstream responses, but no diagnostic HCM2 methylation signature is established.
HCM2 is not caused by pollution, radiation, toxins, occupation, diet, or infection. Environmental/loading factors instead modify expression. Hypertension and obesity add hypertrophic and hemodynamic stress; dehydration and vasodilation may worsen LV outflow obstruction; intense adrenergic activation may reveal arrhythmia susceptibility. Mild-to-moderate recreational exercise is generally encouraged, while high-intensity or competitive exercise requires shared decision-making and is discouraged in individuals with major risk markers or significant obstruction. (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12)
Smoking cessation, moderation of alcohol, maintenance of healthy weight, treatment of sleep apnea and hypertension, and avoidance of illicit stimulants are prudent cardiovascular measures, although none has proven TNNT2-specific disease-preventing efficacy.
TNNT2 variant → altered troponin–tropomyosin/actin regulation → increased thin-filament calcium sensitivity and slower calcium release → hypercontractility and impaired lusitropy → energetic demand–supply mismatch and calcium-handling instability → hypertrophic signaling, cardiomyocyte enlargement, disarray, extracellular-matrix remodeling and fibrosis → diastolic dysfunction, obstruction, ischemia, arrhythmia, and occasionally systolic failure.
The I79N study directly found increased calcium sensitivity and reduced Ca²⁺ off-rate. Its abstract reports that these changes caused “beat-to-beat instability and triangulation of the cardiac action potential,” while NPPA, NPPB, Notch, and ECM-remodeling genes were upregulated. (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2)
In Δ160E cardiomyocytes, calcium retention and delayed relaxation activated CaMKIIδ, phospholamban phosphorylation, and dose-dependent NFATc1 nuclear translocation, linking the biophysical lesion to hypertrophic gene expression. Calcium desensitization with epigallocatechin-3-gallate partially rescued relaxation in vitro. (kondo2022humaninducedpluripotentstem pages 1-2)
Recent model work also implicates mitochondrial redox imbalance: increased myofilament calcium sensitivity can uncouple workload from mitochondrial calcium signaling, consume NADPH-dependent antioxidant reserve, increase mitochondrial ROS, trigger spontaneous sarcoplasmic-reticulum calcium release, and slow conduction. This provides both trigger and substrate for arrhythmia, but the 2024 report was preprint-stage and is not yet a clinical biomarker or therapy. (dolder2025experimentalmodelsof pages 36-36)
Single-cell, spatial-transcriptomic, proteomic, metabolomic, or lipidomic signatures specific to TNNT2-HCM2 remain insufficiently validated for clinical use. Current omics findings are largely experimental and variant/model dependent.
The primary organ is the heart (UBERON:0000948), especially left-ventricular myocardium (UBERON:0002084, myocardium; UBERON:0002080, cardiac ventricle). Hypertrophy may involve the interventricular septum, apex, free wall, papillary muscles, and mitral–septal apparatus; dynamic obstruction localizes to the LV outflow tract. Secondary involvement includes left-atrial enlargement, pulmonary venous hypertension, and systemic thromboembolism from atrial fibrillation.
At tissue level, cardiac muscle shows cardiomyocyte hypertrophy, sarcomere/myofiber disarray, small-vessel disease, and interstitial or replacement fibrosis. At subcellular level, the thin filament, calcium-handling apparatus, mitochondria, and hypertrophic-signaling nucleus are implicated. Disease is not lateralized; ventricular distribution may be asymmetric. (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, cai2020establishinganew pages 21-25)
HCM2 is a chronic lifelong genetic predisposition, often clinically silent for years. Onset can occur in childhood, adolescence, or adulthood; penetrance is age-dependent rather than congenital in every carrier. In the 2024 meta-analysis, mean HCM diagnosis age among nonproband carriers was 38 years, and longitudinal family cohorts showed approximately 15% phenotypic conversion over eight years, beginning from a mean age near 16 years. TNNT2 penetrance was approximately 60% in family-screened relatives. (topriceanu2024metaanalysisofpenetrance pages 1-2)
A useful stage model is:
There is no spontaneous genetic remission. Obstruction and symptoms can improve with treatment, but pathogenic-variant status persists. Childhood growth, athletic exposure, pregnancy, hypertension, and aging are clinically important surveillance periods.
Inheritance is usually autosomal dominant, with a 50% transmission probability from a heterozygous affected parent. Penetrance is incomplete and age-dependent, and expressivity is highly variable—even within a family. Genetic anticipation is not established. Germline mosaicism is possible in principle but is not a defining feature; consanguinity is not generally relevant to dominant HCM2. (topriceanu2024metaanalysisofpenetrance pages 1-2)
The classic clinical prevalence of all HCM is approximately 1 in 500, but contemporary genotype/imaging estimates vary. HCM-associated P/LP variants may be more common than clinically expressed disease. HCM2-specific prevalence and incidence per 100,000 are not robustly established, and TNNT2 is a minority cause compared with MYBPC3 and MYH7. (shafaattalab2021mechanismsofarrhythmogenicity pages 1-2, topriceanu2024metaanalysisofpenetrance pages 1-2)
No consistent ethnicity-specific or geographic distribution applies to TNNT2-HCM as a whole. Individual founder alleles may be enriched locally and should be assessed variant by variant. Both sexes inherit variants equally, although clinical expression and outcomes may differ by sex; no reliable HCM2-specific male:female ratio was recovered.
In adults, HCM is generally diagnosed by otherwise unexplained maximum LV wall thickness ≥15 mm; ≥13 mm may support diagnosis in a first-degree relative or known pathogenic-variant carrier. Echocardiography is first-line. Valsalva, standing, or exercise provocation is used to detect latent obstruction when the resting gradient is absent. Cardiac MRI clarifies apical or focal hypertrophy and identifies aneurysm, thrombus, and late-gadolinium-enhancement fibrosis. (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12, nakamura2025cardiacmyosininhibitors pages 2-4)
Baseline evaluation includes history and pedigree, physical examination, 12-lead ECG, ambulatory ECG, echocardiography, exercise testing when appropriate, and CMR. NT-proBNP and cardiac troponin reflect hemodynamic stress/injury and prognosis but are not HCM2-specific diagnostic tests.
Histology, usually available only after myectomy, transplant, or autopsy, may show cardiomyocyte hypertrophy, nuclear enlargement, myofiber disarray, and fibrosis. Biopsy is not routinely needed for typical sarcomeric HCM.
Recommended testing uses a validated cardiomyopathy panel containing definitive HCM genes, including TNNT2, MYBPC3, MYH7, TNNI3, TPM1, ACTC1, MYL2, and MYL3, with phenocopy genes selected by clinical context. Sequencing plus deletion/duplication analysis is preferred. WES/WGS can be useful when panel testing is negative or the phenotype is atypical, but interpretation of deep-intronic, structural, and incidental variants remains challenging. CMA, karyotyping, FISH, mitochondrial DNA, and repeat-expansion testing are not first-line for isolated HCM2 unless syndromic features suggest another diagnosis.
Once a familial TNNT2 P/LP variant is identified, targeted cascade testing is appropriate. Relatives who test negative for that variant can usually be released from serial HCM surveillance; genotype-positive relatives require longitudinal ECG/imaging. A VUS should not be used for predictive testing. Genetic testing supports family screening and phenocopy discrimination but does not replace phenotype-led sudden-death assessment. (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12, nakamura2025cardiacmyosininhibitors pages 2-4)
Exclude hypertensive heart disease, aortic stenosis, athletic remodeling, transthyretin or light-chain amyloidosis, Fabry disease, glycogen-storage disease including PRKAG2 and LAMP2 disorders, mitochondrial disease, RASopathies, and infiltrative/storage disease. Red flags include multisystem disease, conduction disease, pre-excitation, neuropathy, renal dysfunction, low-voltage ECG despite thick walls, and atypical CMR enhancement.
Many patients have normal or near-normal longevity with contemporary surveillance and treatment, but individual risk varies. Major morbid outcomes are ventricular arrhythmia/sudden death, atrial fibrillation and stroke, progressive heart failure, LV apical aneurysm, and end-stage systolic dysfunction.
TNNT2 should not be treated as uniformly malignant: risk is variant- and phenotype-dependent. Nevertheless, thin-filament TNNT2 variants have been associated with sudden death despite mild LVH, and Δ160E has been associated with adverse remodeling and advanced heart failure. (kondo2022humaninducedpluripotentstem pages 1-2, shafaattalab2021mechanismsofarrhythmogenicity pages 1-2)
Prognostic assessment integrates prior cardiac arrest or sustained VT, unexplained syncope, family history of HCM-related sudden death, maximal wall thickness, LV apical aneurysm, LVEF, nonsustained VT, LVOT gradient, left-atrial size, fibrosis/LGE, and age. The ESC HCM Risk-SCD framework considers an ICD at a five-year risk of 4–6% and recommends it at ≥6%, while US guidance uses major risk markers and shared decision-making. (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12)
No TNNT2-specific circulating prognostic biomarker is clinically validated. Genotype is useful context but should not be the sole basis for ICD implantation.
Treatment is phenotype-directed; no approved therapy corrects the TNNT2 allele.
Mavacamten directly reduces cardiac myosin ATPase activity and excessive actin–myosin cross-bridging. In EXPLORER-HCM, 37% versus 17% achieved the primary exercise/NYHA endpoint; post-exercise LVOT gradient fell approximately 36 mmHg more than placebo. In VALOR-HCM, only 17.9% versus 76.8% remained eligible for septal reduction after 16 weeks. (nakamura2025cardiacmyosininhibitors pages 13-14, ottaviani2023revisitingdiagnosisand pages 23-24)
Long-term MAVA-LTE data over a median 166.1 weeks found 77.9% improved by at least one NYHA class, LVOT gradients declined 40.3–55.3 mmHg, and 82.7% reached a Valsalva gradient <30 mmHg. Transient LVEF <50% occurred in 8.7% and resolved after interruption; this necessitates protocolized echocardiographic monitoring and drug-interaction review. (nakamura2025cardiacmyosininhibitors pages 16-18)
Aficamten, a shorter-half-life myosin inhibitor, reduced LVOT gradients by approximately 27–53 mmHg in REDWOOD/FOREST studies and improved exercise capacity and symptoms in obstructive HCM. These agents treat the HCM physiology, not specifically TNNT2-HCM, and are not curative. (hou2025cardiacmyosininhibitors pages 12-13, ottaviani2023revisitingdiagnosisand pages 23-24)
Mavacamten is teratogenic and contraindicated in pregnancy; reproductive counseling and effective contraception are required. (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12)
Severe drug-refractory symptomatic LVOTO is treated with surgical septal myectomy or, in selected adults, alcohol septal ablation. A contemporary synthesis reported obstruction control in approximately 88% after myectomy and 79% after alcohol ablation; center expertise is crucial. (nakamura2025cardiacmyosininhibitors pages 11-13)
An implantable cardioverter-defibrillator is indicated after cardiac arrest/sustained VT and considered for primary prevention according to risk markers. Heart transplantation is reserved for refractory end-stage disease.
Calcium desensitizers, allele-specific silencing, RNA therapy, gene editing, and gene replacement remain preclinical for TNNT2-HCM. Epigallocatechin-3-gallate rescued calcium-decay abnormalities in Δ160E iPSC cardiomyocytes, but there is no clinical efficacy evidence. (kondo2022humaninducedpluripotentstem pages 1-2)
Primary prevention of the inherited allele is not possible after conception. Reproductive options include genetic counseling, prenatal diagnosis, and preimplantation genetic testing when a familial P/LP variant is known.
Secondary prevention centers on cascade genetic testing, serial ECG/echo surveillance of genotype-positive relatives, early recognition of obstruction/arrhythmia, ambulatory rhythm monitoring, and periodic CMR when clinically indicated. Population or newborn screening is not standard.
Tertiary prevention includes sudden-death risk assessment and ICD placement, anticoagulation for atrial fibrillation, management of obstruction and heart failure, avoidance of dehydration and stimulants, and individualized exercise plans. Mild-to-moderate exercise is generally beneficial; blanket inactivity is not recommended. (sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12)
Vaccination has no disease-specific role beyond routine cardiovascular health. There is no infectious prophylaxis or environmental-control program specific to HCM2.
Naturally occurring cardiomyopathies occur in cats and other animals, but a well-established, breed-specific naturally occurring TNNT2-HCM2 orthologous disease was not identified in the retrieved evidence. Therefore no VBO breed annotation should be asserted without OMIA-level verification. The disease is noninfectious and nonzoonotic.
Orthologous troponin-T biology is highly conserved. A CRISPR-generated zebrafish tnnt2a RK94del heterozygote developed early diastolic dysfunction and abnormal calcium dynamics by five days postfertilization; adults showed atrial enlargement, reduced ventricular size, myocardial stress, fibrosis, and progressive heart failure. This experimentally induced model supports cross-species conservation of thin-filament calcium dysregulation. (kamel2021aheterozygousmutation pages 1-2)
The most important 2023–2024 advance is recognition that genetic HCM penetrance depends strongly on ascertainment. The January 2024 Circulation meta-analysis reviewed 455 manuscripts and estimated TNNT2 penetrance near 60% in cascade-screened relatives, but only about 11% penetrance for incidentally identified sarcomeric P/LP variants in population studies. This supports expert recommendations that genotype be interpreted alongside pedigree and longitudinal phenotype rather than deterministically. DOI: https://doi.org/10.1161/CIRCULATIONAHA.123.065987, published January 2024. (topriceanu2024metaanalysisofpenetrance pages 1-2)
The 2023–2024 guideline era also normalized moderate exercise, emphasized shared ICD decisions and CMR fibrosis assessment, and incorporated cardiac myosin inhibition for symptomatic obstructive HCM. However, these advances are not genotype-specific, and no evidence yet shows that TNNT2 carriers respond differently from other sarcomeric-HCM patients. (nakamura2025cardiacmyosininhibitors pages 13-14, sanghvi2025hypertrophiccardiomyopathymanagement pages 11-12)
The central expert interpretation is therefore: TNNT2 genotype establishes cause and enables cascade screening, but surveillance, prognosis, and treatment remain phenotype-led. Variant-level functional data can be highly informative, yet should not be generalized across all TNNT2 alleles. The largest unresolved needs are variant-specific natural-history cohorts, validated polygenic/environmental modifiers, mature human myocardial models, and trials of causal RNA or gene therapies.
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Checked with linkml-reference-validator 0.2.1.
| Outcome | Count |
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| References checked | 11 |
| Resolved | 11 |
| Unresolved (possible confabulation) | 0 |
| Unverifiable | 0 |
| References weighed for topical relevance | 11 |
| On topic | 7 |
| Off topic | 0 |
All extracted references resolved successfully.